1. Field of the Invention
The present invention relates to a device for feeding a continuous form into a printer for printing. More particularly, the present invention relates to a form feeding device by which errors generated during the feeding of the continuous form are eliminated.
2. Description of the Related Art
The continuous form referred to in this specification is a fan-fold paper form which is a foldable and is provided with sprocket holes, and is constructed in such a manner that the folding portions thereof correspond to perforations by which the continuous form is easily separated into individual pages. This kind of continuous form is usually printed with ruled lines extending in a direction perpendicular to a feeding direction, at predetermined intervals, and the sprocket holes and these ruled lines have a predetermined positional relationship to each other.
Generally, when a continuous form is fed into a printer, errors in the amount of continuous form fed may occur due to an incorrect diameter of a feed roller, an expansion or contraction of the continuous form due to changes of temperature or humidity, or errors in pulses from the pulse motor for driving the device.
In the case of a printer printing each page individually, any errors in the feed amount causes a problem only for the page being printed, and have no influence on the printing of the next page, and thus a small error is permissible. In the case of a printer printing a continuous form, however, any error occurring in one page is accumulated in the following pages, one after another, and thus the error finally exceeds the allowable range. This causes a problem in that the printing is not aligned with the ruled lines.
To solve this problem, the printer may be constructed in such a manner that a width of a pulse operating the pulse motor for driving the feed roller can be adjusted. The width of a pulse is adjusted by a timer by which the width of the pulse is defined. Note, currently a microcomputer is usually used for controlling the printer, and the timer is controlled in accordance with clock signals from the microcomputer.
Assuming that the pulse width is 1 ms, to ensure an accurate printing, the width must be adjusted to an accuracy of about 0.1% of the width, when corrected by the timer. Accordingly, 1 count of the timer is set to 1 .mu.s, and therefore, a timer having 10 bits must be provided to count 1 ms, since 10 bits can count 2.sup.10 (1024).
Thus, if an improvement of the accuracy of adjusting the pulse width is intended, a large number of bits is required for the timer. Nevertheless, the number of bits able to be used for the timer is usually limited, for reasons of economy, and thus it is difficult to provide a timer able to carry out such corrections with a high accuracy.